A novel approach for purifying food waste anaerobic digestate through bio-conditioning dewatering followed by activated sludge process: A case study

Although anaerobic digestion is the mainstream technology for treating food waste (FW), the high pollutant concentration in the resultant food waste anaerobic digestate (FWAD) often poses challenges for the subsequent biochemical treatment such as activated sludge process. In this study, taking a typical FW treatment plant as an example, we analyzed the reasons behind the difficulties in treating FWAD and tested a novel process called as bio-conditioning dewatering followed by activated sludge process (BDAS) to purify FWAD. Results showed that high concentrations of suspended solids (SS) (16439 ± 475 mg/L), chemical oxygen demand (COD) (24642 ± 1301 mg/L), and ammonium nitrogen (NH4+-N) (2641 ± 52 mg/L) were main factors affecting the purification efficiency of FWAD by the conventional activated sludge process. By implementing bio-conditioning dewatering for solid-liquid separation, near 100% of SS and total phosphorus (TP), 90% of COD, 38% of total nitrogen (TN), and 37% of NH4+-N in the digestate could be effectively removed or recovered, consequently generating the transparent filtrate with relatively low pollution load and dry sludge cake (<60% of moisture content). Furthermore, after ammonia stripping and biochemical treatment, the effluent met the relevant discharge standards regulated by China, with the concentrations of COD, TN, NH4+-N, and TP ranging from 151 to 405, 10-56, 0.9-31, and 0.4-0.8 mg/L, respectively. This proposed BDAS approach exhibited stable performance and low operating costs, offering a promising solution to purify FWAD in practical engineering and simultaneously realize resource recovery.

Treatment of pharmaceutical wastewater through activated sludge process-a critical review

The occurrence of pharmaceutical compounds in water is a rising issue in the environment. These drugs in the waste may be toxic to aquatic organisms and humans as they disrupt the endocrine system, cause genotoxicity, etc. Several techniques were used for the treatment of pharmaceutical wastewater, such as physical, chemical, physiochemical, and biological processes like adsorption, chemical coagulation, and activated sludge processes, but these techniques possess several merits and demerits, such as higher installation and operation costs. This technique is used to remove color and turbidity; reduce biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total suspended solids (TSS) to permissible limits for reuse of effluent; and prevent diseases caused by pharmaceutical wastewater. This review focuses on the treatment of pharmaceutical wastewater containing drugs like antibiotics, depressants, and hormones, with the activated sludge process having several advantages like good quality effluent and low installation costs.

Wastewater treatment plant performance assessment using time-function-based effluent quality index and multiple regression models: the case of Bahir Dar textile factory

Extensive water and chemicals are used in the textile industry processes. Therefore, treatment of textile wastewater is vital to protect the environment, maintain the public health, and recover resources. However, due to poor operation and plant performance the partially treated textile wastewater was directly discharged to a nearby river. Thus, the aim of this study was to characterize the wastewater physicochemical properties and evaluate the performance of the textile factory-activated sludge process wastewater treatment plant (WWTP) in Bahir Dar, Ethiopia. In inlet and outlet of the WWTP, samples were collected for 6 months and analyzed on-site and in a laboratory for parameters including, dissolved oxygen, pH, temperature, total Kjeldhal nitrogen (TKN), chemical oxygen demand (COD), biochemical oxygen demand (BOD5), total suspended solids (TSS), total nitrogen (TN), total phosphorous (TP), nitrite, nitrate, and metallic compounds. The TSS, BOD5, COD, TP, nitrite, ammonia, and total chromium result were above the discharge limit with 73.2 mg/L, 48.45 mg/L, 144.08 mg/L, 7.9 mg/L, 1.36 mg/L, 1.96 mg/L, and 0.16 mg/L, respectively. Multiple regression models were developed for each overall, net moving average, and instantaneous effluent quality index (EQI). The predictor parameters BOD5, TN, COD, TSS, and TP (R2 = 0.995 to 1.000) estimated the net pollution loads of all predictors as 492.55 kg/day and 655.44 kg/day. Except TN, TKN, and NO3, the remaining six performance parameters were violating the permissible limit daily. Furthermore, the overall plant efficiency was predicted as 38 % and 42 % for the moving average and instantaneous EQI, respectively. Our study concluded that the integrated regression models and EQI can easily estimate the plant efficiency and daily possible pollution load.

A review of filamentous sludge bulking controls from conventional methods to emerging quorum quenching strategies

Filamentous bulking, which results from the overgrowth of filamentous microorganisms, is a common issue that frequently disrupts the stable operation of activated sludge processes. Recent literature has paid attention to the relationship between quorum sensing (QS) and filamentous bulking highlighting that the morphological transformations of filamentous microbes are regulated by functional signal molecules in the bulking sludge system. In response to this, a novel quorum quenching (QQ) technology has been developed to control sludge bulking effectively and precisely by disturbing QS-mediated filamentation behaviors. This paper presents a critical review on the limitations of classical bulking hypotheses and traditional control methods, and provides an overview of recent QS/QQ studies that aim to elucidate and control filamentous bulking, including the characterization of molecule structures, the elaboration of QS pathways, and the precise design of QQ molecules to mitigate filamentous bulking. Finally, suggestions for further research and development of QQ strategies for precise bulking control are put forward.

Activated carbon enhanced traditional activated sludge process for chemical explosion accident wastewater treatment

With the development of industries, explosion accidents occur frequently during production, transportation, usage and storage of hazard chemicals. It remained challenging to efficiently treat the resultant wastewater. As an enhancement of traditional process, the activated carbon-activated sludge (AC-AS) process has a promising potential in treating wastewater with high concentrations of toxic compounds, chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N), etc. In this paper, activated carbon (AC), activated sludge (AS) and AC-AS were used to treat the wastewater produced from an explosion accident in the Xiangshui Chemical Industrial Park. The removal efficiency was assessed by the removal performances of COD, dissolved organic carbon (DOC), NH₄⁺-N, aniline and nitrobenzene. Increased removal efficiency and shortened treatment time were achieved in the AC-AS system. To achieve the same COD, DOC and aniline removal (90%), the AC-AS system saved 30, 38 and 58 h compared with the AS system, respectively. The enhancement mechanism of AC on the AS was explored by metagenomic analysis and three-dimensional excitation-emission-matrix spectra (3DEEMs). More organics, especially aromatic substances were removed in the AC-AS system. These results showed that the addition of AC promoted the microbial activity in pollutant degradation. Bacteria, such as Pyrinomonas, Acidobacteria and Nitrospira and genes, such as hao, pmoA-amoA, pmoB-amoB and pmoC-amoC, were found in the AC-AS reactor, which might have played important roles in the degradation of pollutants. To sum up, AC might have enhanced the growth of aerobic bacteria which further improved the removal efficiency via the combined effects of adsorption and biodegradation. The successful treatment of Xiangshui accident wastewater using the AC-AS demonstrated the potential universal characteristics of the process for the treatment of wastewater with high concentration of organic matter and toxicity. This study is expected to provide reference and guidance for the treatment of similar accident wastewaters.

Insight into the interaction between trimethoprim and soluble microbial products produced from biological wastewater treatment processes

Soluble microbial products (SMPs), dissolved organic matter excreted by activated sludge, can interact with antibiotics in wastewater and natural water bodies. Interactions between SMPs and antibiotics can influence antibiotic migration, transformation, and toxicity but the mechanisms involved in such interactions are not fully understood. In this study, integrated spectroscopy approaches were used to investigate the mechanisms involved in interactions between SMPs and a representative antibiotic, trimethoprim (TMP), which has a low biodegradation rate and has been detected in wastewater. The results of liquid chromatography-organic carbon detection-organic nitrogen detection indicated that the SMPs used in the study contained 15% biopolymers and 28% humic-like substances (based on the total dissolved organic carbon concentration) so would have contained sites that could interact with TMP. A linear relationship of fluorescent intensities of tryptophan protein-like substances in SMP was observed (R²>0.99), indicating that the fluorescence enhancement between SMP and TMP occurred. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated that carboxyl, carbonyl, and hydroxyl groups were the main functional groups involved in the interactions. The electrostatic and π-π interactions were discovered by the UV-vis spectra and ¹H nuclear magnetic resonance spectra. Structural representations of the interactions between representative SMP subcomponents and TMP were calculated using density functional theory, and the results confirmed the conclusions drawn from the ¹H nuclear magnetic resonance spectra. The results help characterize SMP-TMP complexes and will help understand antibiotic transformations in wastewater treatment plants and aquatic environments.

Activated sludge process enabling highly efficient removal of heavy metal in wastewater

Activated sludge process was a low-cost alternative method compared to the conventional physicochemical process for the treatment of heavy metal-containing wastewater. In the present study, the removal efficiency of Pb²⁺, Cu²⁺, and Ni²⁺ from wastewater by a sequencing batch reactor (SBR) activated sludge system was investigated, and the mechanism was revealed by static adsorption experiment of activated sludge. The results showed that the activated sludge in the SBR system was effective in removing Pb²⁺ and Cu²⁺ from wastewater at 10 mg·L^-1 initial concentration, with a removal efficiency of 83.1 ~ 90.0% for Pb²⁺ and 74.3 ~ 80.6% for Cu²⁺, respectively. However, the removal efficiency for Ni²⁺ was only 0 ~ 6.2%. Static adsorption experiments showed that the adsorption capacity of activated sludge for three heavy metals was shown as Pb²⁺  > Cu²⁺  > Ni²⁺. When the initial concentration was 20 mg·L^-1, the equilibrium adsorption capacity of activated sludge for Pb²⁺, Cu²⁺, and Ni²⁺ was 18.35 mg·g^-1, 17.06 mg·g^-1, and 8.37 mg·g^-1, respectively. The main adsorption mechanisms for Pb²⁺ and Cu²⁺ were ligand exchange, electrostatic adsorption, and surface organic complexation processes, but Ni²⁺ removal mechanism mainly included electrostatic adsorption and surface organic complexation processes, showing that Ni²⁺ removal was inhibited in the presence of Pb²⁺ and Cu²⁺. The physicochemical properties and microbial diversity of activated sludge were greatly affected by the heavy metals in the SBR system, and genus Rhodobacter was found to be dominant bacteria enabling resistance to heavy metal ions.

Fractional-order models identification and control within a supervisory control framework for efficient nutrients removal in biological wastewater treatment plants

Wastewater treatment plants (WWTPs) are highly non-linear processes that must be optimized to meet rigorous environmental water regulations. In this context, efficiency and costs are equally important terms. The ASM3bioP framework is employed in this study to enable simultaneous nitrogen and phosphorus removal using an activated sludge process model with seven-reactor configurations. The activated sludge process is the most complicated and energy-intensive phase of a WWTP. To control dissolved oxygen in aerobic reactors and nitrate levels in anoxic reactors, two robust PI controllers - a classical PI and a non-integer (fractional)-order PI - with both integer-order and fractional-order models are designed. The controllers are created and simulated with the use of a mathematical model that has been developed based on the input data. The lower level fractional controller with a fractional-order model improves both the effluent quality (EQI) and operational cost (OCI) indices significantly. For such biological WWTP, a hierarchical fuzzy logic controller is designed to adjust the dissolved oxygen in the seventh reactor (DO₇) to control ammonia. The implemented supervisory layer control strategy improves effluent quality EQI while increasing OCI marginally.

Retrofitting a full-scale multistage landfill leachate treatment plant by introducing coagulation/flocculation/sedimentation and ultrafiltration process steps

Considering that landfilling still remains among the most commonly used methods for the confrontation of solid wastes, effective methods should be applied to treat the leachate generated, due to its recalcitrant nature. In this work, a full-scale system consisting of two SBRs operating in parallel (350 m³ each) and two activated carbon (AC) columns operating in series (3 m³ each) was retrofitted by introducing a coagulation/flocculation/sedimentation (C/F/S) unit of 7.8 m³ and an ultrafiltration (UF) membrane of 100 m² to effectively treat landfill leachate. The raw leachate was characterized by high COD and NH₄⁺-N concentration, i.e., 3095 ± 706 mg/L and 1054 ± 141 mg/L respectively, a BOD/COD ratio of 0.22, and high concentrations of certain heavy metals. Leachate processing in this retrofitted multistage treatment system resulted in total COD removal efficiency of 89.84%, with biological treatment, C/F, UF, and AC contributing 46.31%, 4.68%, 15.98%, and 22.87% to the overall organic content removal. The retrofitted scheme achieved an overall NH₄⁺-N and TKN removal of 92.03% and 91.75% respectively, attributed mostly to the activity of an effective nitrifying community. Color number (CN) was reduced by 26.96%, 10.29%, 15.94%, and 5.39% after the activated sludge, the C/F, the UF, and the AC adsorption process respectively, corresponding to a 58.91% overall decrease. Regarding heavy metal removal, all elements examined, apart from Ni, i.e., effluent As, Cd, Co, Cr, Cu, Hg, Mg, Mn, and Pb, were below the legislative limits set by the national authorities for restricted or unrestricted irrigation. Lastly, total operating expenses (OPEX) were estimated as equal to 72,687 €/year or 6.64 €/m³.

Microbubble- and nanobubble-aeration for upgrading conventional activated sludge process: A review

The activated sludge process (ASP) is widely used for wastewater treatment, and the aeration efficiency is crucial to the operation of wastewater treatment plants. Recently, microbubble (MB)- and nanobubble (NB)-aeration has attracted much attention as there is growing evidence that it holds a great promise for upgrading the process efficiency of current ASP under conventional macro-bubble-aeration. However, a comprehensive review to elucidate the potential application of MB- and NB-aeration in ASP is still lacking. Therefore, this review will provide a systematic introduction to MB- and NB-aeration (including the unique properties and generation methods of MBs and NBs), and gain mechanistic insights on how MB- and NB-aeration improve gas-liquid mass transfer. The recent advances in MB- and NB-aeration applications to ASP and the resultant effects are also highlighted and discussed in-depth. The review concludes with a brief consideration of future research interests.

Simultaneous denitrification and phosphorus removal: A review on the functional strains and activated sludge processes

Eutrophication has attracted extensive attention owing to its harmful effects to the organisms and aquatic environment. Studies on the functional microorganisms with the ability of simultaneously nitrogen (N) and phosphorus (P) removal is of great significance for alleviating eutrophication. Thus far, several strains from various genera have been reported to accomplish simultaneous N and P removal, which is primarily observed in Bacillus, Pseudomonas, Paracoccus, and Arthrobacter. The mechanism of N and P removal by denitrifying P accumulating organisms (DPAOs) is different from the traditional biological N and P removal. The denitrifying P removal (DPR) technology based on the metabolic function of DPAOs can overcome the problem of carbon source competition and sludge age contradiction in traditional biological N and P removal processes and can be applied to the treatment of urban sewage with low C/N ratio. This paper reviews the mechanism of N and P removal by DPAOs from the aspect of the metabolic pathways and enzymatic processes. The research progress on DPR processes is also summarized and elucidated. Further research should focus on the efficient removal of N and P by improving the performance of functional microorganisms and development of new coupling processes. This review can serve as a basis for screening DPAOs with high N and P removal efficiency and developing new DPR processes in the future.

Transcriptomic response of HepG2 cells exposed to three common anti-inflammatory drugs: Ketoprofen, mefenamic acid, and diclofenac in domestic wastewater effluents

The biological impacts of residual pharmaceuticals in the complex wastewater effluents have not been fully understood. Here, we investigated changes in the transcriptomic responses of hepatobrastoma (HepG2) cells exposed to a single or partially combined three common non-steroidal anti-inflammatory drugs (NSAIDs); ketoprofen (KPF), mefenamic acid (MFA) and diclofenac (DCF), in domestic wastewater effluents. After 48 h sub-lethal exposure to single compounds, the DNA microarray analysis identified 57-184 differently expressed genes (DEGs). The hierarchical clustering analysis and GO enrichment of the DEGs showed that gene expression profiles of the NSAIDs were distinct from each other although they are classified into the same therapeutic category. Four maker genes (i.e., EGR1, AQP3, SQSTM1, and NAG1) were further selected from the common DEGs, and their expressions were quantified by qPCR assay in a dose-dependent manner (ranging from μg/L to mg/L). The results revealed the insignificant induction of the marker genes at 1 μg/L of KPF, MFA, and DCF, suggesting negligible biological impacts of the NSAIDs on gene expression (early cellular responses) of HepG2 at typical concentration levels found in the actual wastewater effluents. Based on the quantitative expression analysis of the selected marker genes, the present study indicated that the presence of wastewater effluent matrix may mitigate the potentially adverse cellular impacts of the NSAIDs.

A review of antibiotic removal from domestic wastewater using the activated sludge process: removal routes, kinetics and operational parameters

Many advanced technologies have shown encouraging results in removing antibiotics from domestic wastewater. However, as activated sludge treatment is the most common sewage treatment system employed worldwide, improving its effect on antibiotic removal would be more desirable. Understanding the removal mechanisms, kinetics and factors that affect antibiotic removal in the activated sludge process is important as it would allow us to improve the treatment performance. Although these have been discussed in various literature covering different types of antibiotics and wastewater, a specific review on antibiotics and domestic wastewater is clearly missing. This review paper collates, discusses and analyses the removal of antibiotics from sewage in the activated sludge process along with the removal mechanisms and kinetics. The antibiotics are categorised into six classes: β-lactam, dihydrofolate reductase inhibitor, fluoroquinolone, macrolide, sulfonamides and tetracycline. Furthermore, the factors affecting the system performance with regard to antibiotic removal are examined.

Reduction of ozone dosage by using ozone in ultrafine bubbles to reduce sludge volume

Sludge ozonation, which promotes sludge disintegration and solubilization, is a promising technology for reducing waste sludge volume from biological wastewater treatment process. However, if this technology is to be widely adopted, reducing the energy consumption associated with ozone generation will be necessary. We used ultra-fine bubbles (UFBs) as ozone carriers to determine if their use could improve the efficiency of ozone treatment and reduce the ozone dose required. We used a spiral, liquid-type UFB generator, which can introduce UFBs directly into a sludge suspension. The death ratio of bacteria in sludge was used as an indicator of sludge reduction. The ozone requirement was reduced by UFBs. The ozone consumption required to achieve a death ratio of 80% was 15 mg-O₃/g-MLSS in the sludge treated with ozone supplied by UFBs versus 25 and 45 mg-O₃/g-MLSS in sludges treated with ozone supplied as a spiral, liquid-type microbubbles and by a diffuser, respectively. When mixing water ozonated with UFBs with sludge, the depth of the dead cell layer from the surface to the interior of the sludge floc was larger than that of ozonated water lacking UFBs at the same rate of ozone consumption. Ozone in UFBs kills bacteria inside the flocs. However, the fragmentation of sludge flocs by shear forces in the UFB generator made a larger contribution to the acceleration of bacterial death in sludge treated with ozone supplied by UFBs.

Organic and nitrogenous pollutants removal paths in vegetation activated sludge process (V-ASP) for decentralized wastewater treatment by using stable isotope technique

The organics (C) and nitrogenous (N) pollutants removal paths by functional units in vegetation-activated sludge process (V-ASP) were investigated by using stable isotope probing and high-throughput sequencing for the first time. V-ASP system displayed superior treatment performance compared to conventional activated sludge system, as manifested by its greater C and N removal efficiencies, higher abundance of denitrifying and heterotrophic functional Genus, and better resistance to low temperature. Isotope δ¹³C and δ¹⁵N were continuously accumulated in plant roots allocated in the V-ASP, where suspended sludge demonstrated obviously higher C and N enrichment rates compared to the rhizosphere sludge. The mass balance estimation showed that bacterial dissimilation was the dominant removal paths for C (54.13%) and N (47.53%). The underlying pollutants removal paths evidenced the advantageous of V-ASP that is a high feasible and promising approach for decentralized wastewater treatment process.

Magnesium ferrite spinels as anode modifier for the treatment of Congo red and energy recovery in a single chambered microbial fuel cell

Magnesium Ferrite (MgFe₂O₄) spinel structures prepared by a solid-state reaction was used as an anode modifier in the microbial fuel cell (MFC) treatment of Congo red dye. The performance of the reactors with unmodified stainless-steel mesh anode (CR-1) and MgFe₂O₄ coated stainless steel mesh anode (CR-2) were tested and compared followed by aerobic treatment. The peak power density was observed to be 295.936 (CR-1) and 430.336 mW/m² (CR-2) revealing increased bioenergy output and better electron transfer in the reactor with the MgFe₂O₄ modified anode. The final decolourisation efficiencies were found to be 92.053% for CR-1 and 98.386% for CR-2. The formation of metabolites (diaminonaphthalene-1-sulfonate, 1-(biphenyl-4-yl)-2-(naphthalene-2-yl) diazene, benzidine and phthalic acid, monoethyl ether) during the anaerobic-aerobic biotreatment of azo dye was confirmed using Gas chromatography coupled Mass spectrometry system. Scanning electron microscopy confirmed a uniform coating of MgFe₂O₄ on the anode surface with evidence of biofilm formation in the system. Electrochemical studies confirmed the superior performance of spinel coated anode with enhanced redox activity. In addition, the charge-discharge studies confirmed the high capacitive nature of the modified electrode improving the electrodes charge holding capacity. The study suggested an effective treatment strategy for the treatment of Congo red dye.

Occurrence and removal of 17α-ethynylestradiol (EE2) in municipal wastewater treatment plants: Current status and challenges

As a synthetic estrogen, 17α-ethynylestradiol (EE2) has been known to show the strong estrogenic potency. This work critically reviewed the occurrence and removal of EE2 in municipal wastewater treatment plants (WWTPs). Based on the on-site investigations from 282 municipal WWTPs across 29 countries, the concentrations of EE2 in influent and effluent ranged from n.d-7890 and n.d-549 ng/L, with respective average concentrations of 78.4 and 12.3 ng/L. The average effluent concentration of EE2 was more than 61 times higher than the reported lowest-observed-effect concentration, indicating an urgent need for removing EE2 in WWTPs. The calculated removal efficiencies of EE2 in different wastewater treatment processes varied from -100%-100%. Averagely, 47.5% of EE2 was removed in the primary treatment process, 55.3% by biological filter treatment, 59.4% by lagoon and 71.5% by activated sludge process. The observed removal of EE2 in municipal WWTP could be mainly attributed to adsorption and biodegradation, which could be predicted according to its solid-water distribution coefficients and biodegradation rate constants. However, it should be noted that the predicted removal of EE2 was found to deviate from the in-plant observation, likely attributing to the existence of EE2 conjugates in raw municipal wastewater. Therefore, the effect of EE2 conjugates on the EE2 removal in WWTPs should be taken into account in future.

Observer based robust H ∞ fuzzy tracking control: application to an activated sludge process

The design of an observer-based robust tracking controller is investigated and successfully applied to control an Activated Sludge Process (ASP) in this study. To this end, the Takagi-Sugeno (TS) fuzzy modeling is used to describe the dynamics of a nonlinear system with disturbance. Since the states of the system are not fully available, a fuzzy observer is designed. Based on the observed states and a reference state model, a reduced fuzzy controller for trajectory tracking purposes is then proposed. While the controller and the observer are developed, the design goal is to achieve the convergence and a guaranteed H _∞ performance. By using Lyapunov and H _∞ theories, sufficient conditions for synthesis of a fuzzy observer and a fuzzy controller for TS fuzzy systems are derived. Using some special manipulations, these conditions are reformulated in terms of linear matrix inequalities (LMIs) problem. Finally, the robust and effective tracking performance of the proposed controller is tested through simulations to control the dissolved oxygen and the substrate concentrations in an activated sludge process.

Design of control strategies for nutrient removal in a biological wastewater treatment process

Wastewater treatment plants (WWTP) are highly non-linear operations concerned with huge disturbances in flow rate and concentration of pollutants with uncertainties in the composition of influent wastewater. In this work, the activated sludge process model with seven reactor configuration in the ASM3bioP framework is used to achieve simultaneous removal of nitrogen and phosphorus. A total of 8 control approaches are designed and implemented in the advanced simulation framework for assessment of the performance. The performance of the WWTP (effluent quality index and global plant performance) and the operational costs are also evaluated to compare the control approaches. Additionally, this paper reports a comparison among proportional integral (PI) control, fuzzy logic control, and model-based predictive control (MPC) configurations framework. The simulation outcomes indicated that all three control approaches were able to enhance the performance of WWTP when compared with open loop operation.

Effectiveness of helminth egg reduction by solar drying and liming of sewage sludge

The present study is aimed at assessing the effectiveness of solar drying process in terms of helminth egg reduction in sewage sludge (SS) generated from an activated sludge wastewater treatment plant (WWTP) in Marrakesh city (Morocco). It is also engaged to highlight a synergic effect of liming (1% CaO) and solar drying on helminth egg reduction. The solar drying process was conducted for 45 days, in summer under a semi-arid climate in a pilot scale polycarbonate-based tunnel (2 m³). Before undergoing solar drying process, data showed an important load of helminth eggs including Ascaris sp., Schistosoma spp., Capillaria spp., Trichuris spp., Ankylostome spp., Toxocara spp., and Taenia spp. in limed sludge (LS) and non-limed sludge (NLS) (15.2 and 17.9 eggs/g, respectively). Ascaris eggs were the most abundant (11.2 and 13.5 eggs/g in LS and NLS, respectively). By the end of the solar drying process, a considerable removal of the total helminth eggs was recorded in LS and NLS (92.8% and 91.6%, respectively). A complete removal of Schistosoma spp., Capillaria spp., Trichuris spp., Toxocara spp. and Taenia spp. was noted in LS and NLS. In the case of Ankylostome spp., data showed a total removal in LS and 81% in NLS; however, the final load is in agreement with the standards (0.4 egg/g). As for Ascaris spp., neither liming nor solar drying process allowed a complete removal (91% and 90% in NLS and LS, respectively) and the final load (1.1 egg/g) does not fulfill the WHO requirements for an agricultural use. Principal component analysis (PCA) demonstrated a negative correlation between dry matter (DM) content (hence temperature) and helminth egg concentration. No significant synergic effect of liming and solar drying process was showed by statistical analysis. This is substantiating that temperature is the key parameter involved in helminth egg removal while undergoing solar drying of SS.

Effects of hydrodynamic shear stress on sludge properties, N2O generation, and microbial community structure during activated sludge process

Sludge properties are critical to the treatment performance and potentially correlate with nitrous oxide (N₂O) generation during activated sludge processes. The hydrodynamic shear stress induced by aeration has a significant influence on sludge properties and is inevitable for wastewater treatment plants (WWTPs). In this study, the effects of aerobic induced hydrodynamic shear stress on sludge properties, N₂O generation, and microbial community structure were investigated using three parallel sequencing batch reactors (SBRs) with identical dissolved oxygen (DO) concentrations. Results showed that with a shear stress increase from 1.5 × 10^-2 N/m² to 5.0 × 10^-2 N/m², the COD and NH₄⁺-N removal rates were enhanced from 89.4% to 94.0% and from 93.9% to 98.0%, respectively, while the TN removal rate decreased from 66.0% to 56.5%. Settleability of the activated sludge flocs (ASFs) also increased with the enhancement of shear stress, due to variation in sludge properties including particle size, regularity, compactibility, and EPS (extracellular polymeric substances) composition. The increase in shear stress promoted oxygen diffusion within the ASFs and mitigated NO₂^--N accumulation, leading to a decrease in the N₂O-N conversion rate from (4.8 ± 0.3)% to (2.2 ± 0.6)% (based on TN removal). Microbial analysis results showed that the functional bacteria involved in the biological nitrogen removal was closely related with shear stress. The increase in shear stress favored the enrichment of nitrite oxidizing bacteria (NOB) while suppressed the accumulation of ammonia-oxidizing bacteria (AOB) and denitrifying bacteria (DNB).

Selection of optimum biological treatment for coking wastewater using analytic hierarchy process

The design of biological treatment process for the coking wastewater (CW) is complicated since wastewater treatment demand is gradually increasing lacking the systematic strategy in efficiency evaluation and advisable selection. Therefore, this study develops a holistic approach by means of the analytic hierarchy process (AHP) that uses numerical representation to rank the preferences of each participating alternatives for evaluation of the advanced biological technologies in CW treatment. Based on survey results, six types reactor combinations were selected as the alternatives, which were further classified as two group according to COD load. The AHP methodology consists of weighting and ranking procedures considering technical, economic, environmental and administration factors defined as criteria layers. Eighteen indicators were chosen as sub-criteria layers. Inclusively beneficial and sustainable biological processes were assessed and ranked along the AHP implementation. The results placed technical indicators to the top position among the criteria layers in the weighting descending order 'technical indicators > economic indicators > environmental indicators > administrative indicators', whereas the weight of indicators in sub-criteria layers fitted in the range of 0.005 to 0.151. The inclusive priority calculation integrating all weight indices of criteria and sub-criteria layers resulted in the anaerobic-anoxic-oxic (A/A/O) combination rising in the hierarchy of the low load group, whereas the oxic-hydrolytic-oxic (O/H/O) process was prioritized in the high load group. The accuracy and objectivity of AHP application was also supported by sensitivity and variability analyses that examines a range for the weights' values and corresponding to alternative scenarios.

Effects of exogenous N-acyl-homoserine lactones on nutrient removal, sludge properties and microbial community structures during activated sludge process

This study investigated the effects of exogenous N-acyl-homoserine lactone (AHL) signal molecules, N-hexanoyl-_l-homoserine lactone (C6-HSL) and N-octanoyl-_l-homoserine lactone (C8-HSL), on treatment performance, sludge properties and microbial community structures in activated sludge systems. Results showed that the nitrification and denitrification efficiencies were enhanced with the addition of signal molecules. The particle size, irregularity, and internal mass transfer resistance of activated sludge flocs (ASFs) increased, primarily because dosing AHLs led to a content increase and chemical composition variation of extracellular polymeric substances (EPS) in sludge. Microbial analysis indicated an increase in both the bacterial richness and diversity of the systems. The relative abundances of the key functional groups, including bacteria related to C and N removal and EPS production, varied correspondingly. This study presents an insight into the comprehensive understanding of the effects of AHL-based quorum sensing on activated sludge treatment process.

Minimizing greenhouse gas emission from wastewater treatment process by integrating activated sludge and microalgae processes

A novel integrated microalgae and activated sludge (MA/AS) system was constructed to minimize greenhouse gas emission from traditional wastewater treatment plants. Its removal properties for aqueous pollutants were assessed as well. The ratio of microalgae-to-activated sludge volatile suspended solids of 1.3 and an incident light intensity of 12 W/m² provided the best performance: COD, NH₄⁺, and total phosphorus (TP) removals were up to 100%, 99.6% and 100%, respectively. Even without illumination, COD, NH₄⁺, and TP removal efficiencies were as high as 95.1%, 96.5% and 100%, respectively. In both cases, nutrient uptake by MA was proved to play an important role in nutrients removal. And no CH₄ or N₂O emissions were detected during the whole experimental period of the MA/AS system (mass ratio of 1.3:1). Only negligible CO₂ was detected up to 45 μmol with illumination and 130 μmol without illumination in the headspace of the serum bottles, which merely accounted for 2.0% and 5.8% of the initial total carbon equivalent (glucose serving as organic carbon source). Since photosynthesis by microalgae could provide oxygen to heterotrophs or nitrifying bacteria, extra energy demand (mainly from aeration units) could be greatly cut down, which would heavily reduce the total energy demands and further indirect CO₂ emission from wastewater treatment plants. Our integrated system is demonstrated to be a sustainable approach for contaminants removal from aqueous phase, restraining greenhouse gas emission and saving energy consumption contemporaneously.

Monitoring microbial community structure and variations in a full-scale petroleum refinery wastewater treatment plant

This research investigated the process efficiency and microbial communities and their diversity in a full-scale wastewater treatment plant (WWTP) fed with petroleum refining wastewater (PRW) that contained toxic hydrocarbon contaminants and carcinogens. Process parameters and bacterial community structures were monitored for six months to create a link between microbial dynamics and influent characteristics of petrochemical wastewater. The WWTP showed a stable process with efficiencies >70% for both soluble chemical oxygen demand (SCOD) and benzene removal. More than 30 genera were identified by metagenomic analysis, and the bacterial populations changed significantly during the operation period. Among them, genera Sulfuritalea (11.9 ± 3.5%), Ottowia (4.3 ± 2.2%), Thauera (3.1 ± 7.2%) and Hyphomicrobium (1.3 ± 0.7%) were dominant and important bacterial genera that may have been responsible for the degradation of aromatic compounds such as benzene and phenol.

The effect of hydraulic retention time on microalgae-based activated sludge process for Wupa sewage treatment plant, Nigeria

This study evaluated the efficiency of microalgae activated sludge (MAAS) for wastewater treatment by investigating the influence of hydraulic retention time (HRT) on MAAS using batch regime pilot scale photobioreactors at Wupa Wastewater Treatment Plant. The outcome of the study showed that MAAS has a comparably high wastewater treatment performance in comparison with the current Wupa Wastewater Treatment Plant (WWTPA) activated sludge (AS) method and is capable of treating wastewater to the defined Nigerian effluent standards. It was further revealed that treatment performance for most parameters were optimal from HRT₃ (6-day hydraulic retention time). Precisely, total nitrogen (TN), total phosphorus (TP), and BOD₅ had highest removal efficiency at HRT₃ with average total removal of 81.36%, 91.77% and 87.04% respectively. Correspondingly, the average percentage DO increment peaked at HRT₃ with a value of 269.7%. In addition, there was a general deterioration of SVI with increasing HRT, particularly after HRT₂ (4-day HRT). Notably, SVI₃₀ was significantly good at HRT₁ and HRT₂ with SVI values of 48.6 ml/g and 105.52 ml/g; however, from HRT₃ down to HRT₉, the SVI₃₀ became remarkably increases greater than that of HRT₁ and HRT₂, with values ranging from 685.61 to 1832.46 ml/g, which indicates a badly bulking sludge. The MAAS system is recommended as an attractive alternative to the conventional AS wastewater treatment in Nigeria and by extension West African subregion.

Assessing biomass diversity and performance of an activated sludge process treating saline table olive processing wastewater

This study aimed to determine the effects of salinity on the biomass behavior and its diversity in activated sludge process (ASP) treating the table olive processing wastewater (TOPW), and to evaluate ASP performances under increased TOPW concentration feeding, the numerical abundance, diversity and activity of the biomass, removal efficiencies of chemical oxygen demand (COD), phenolic compounds, nitrogen and phosphorus were evaluated. Results showed that biomass growth is very high and became faster according to an increase in the percentage of TOPW feeding and reached 5.2 g_MLVSS l^-1. The specific oxygen uptake rate (SOUR) analysis revealed that salinity up to 10 g l^-1 provides an increase in biomass activity. SOUR reached a maximum of 20.3 g_O2 g_MLVSS^-1 h^-1. The increasing percentages of TOPW induce actually an evolution of microorganism's biodiversity; the microorganism communities were characterized by the abundance of halotolerant, Pseudomonas and Yeast genus that became the most abundant in the bioreactor as adaptation response against salinity. Furthermore, COD, phenolic compounds, nitrogen and phosphorus removal efficiencies attained 92.3%, 84.5%, 80% and 60%, respectively. A satisfactory release of extracellular polymeric substances is found to occur in the reactor with regard to increased saline TOPW, providing significant removal efficiencies and best settling of sludge.

Energy self-sufficient biological municipal wastewater reclamation: Present status, challenges and solutions forward

Almost all present biological processes for treating municipal wastewater have been developed based on the philosophy of biological oxidation with high energy consumption and generation of waste sludge. Given such a situation, the fundamental question of what are the possible ways towards energy self-sufficient biological reclamation of municipal wastewater needs to be addressed urgently. Therefore, this review aims to offer a critical view and a holistic analysis of biological treatment processes with the focus on energy self-sufficiency which indeed is a game changer in the future technology development. The way towards energy self-sufficient operation of biological processes is to maximize energy recovery, while to minimize energy consumption. The examples of such process configurations known as A-B processes are thus discussed. Consequently, this review may offer in-depth insights into the possible directions towards the next-generation biological processes for municipal wastewater reclamation which should be designed as a water-energy-resource factory.

Behavior of tetracycline and macrolide antibiotics in activated sludge process and their subsequent removal during sludge reduction by ozone

Ozonation is a promising means for the reduction of excess sludge in wastewater treatment plants. However, little information is available on the removal of antibiotics during sludge ozonation. Therefore, this study investigated first the behavior of four commonly-used hydrophobic antibiotics, including three tetracyclines (tetracycline, oxytetracycline, and doxycycline) and one macrolide (azithromycin) in activated sludge process and then their removal during sludge reduction by ozone. Results indicate that the studied antibiotics were primarily transferred into the solid phase of activated sludge via sorption, which was a reversible, spontaneous, and exothermic process governed by surface reactions. Sludge ozonation could effectively remove 86.4-93.6% of the antibiotics present in the sludge at an ozone dose of 102 mg per gram of mixed liquor suspended solids and pH 7.2. The removal of studied antibiotics mainly proceeded through desorption and subsequent oxidation. Increasing the initial pH from 5.0 to 9.5 obviously enhanced the antibiotic removal during sludge ozonation. This study demonstrated that the activated sludge process coupled with sludge ozonation can simultaneously reduce excess sludge and eliminate antibiotics.

Comparison of modelling accuracy with and without exploiting automated optical monitoring information in predicting the treated wastewater quality

Traditionally the modelling in an activated sludge process has been based on solely the process measurements, but as the interest to optically monitor wastewater samples to characterize the floc morphology has increased, in the recent years the results of image analyses have been more frequently utilized to predict the characteristics of wastewater. This study shows that the traditional process measurements or the automated optical monitoring variables by themselves are not capable of developing the best predictive models for the treated wastewater quality in a full-scale wastewater treatment plant, but utilizing these variables together the optimal models, which show the level and changes in the treated wastewater quality, are achieved. By this early warning, process operation can be optimized to avoid environmental damages and economic losses. The study also shows that specific optical monitoring variables are important in modelling a certain quality parameter, regardless of the other input variables available.

Parameter estimation of activated sludge process based on an improved cuckoo search algorithm

It is essential to use appropriate values for kinetic parameters in activated sludge model when the model is applied for wastewater treatment processes under different environments. An improved cuckoo search (ICS) algorithm was proposed in this paper for the estimation of kinetic parameters used in Activated Sludge Model No. 1 (ASM1). ICS is tested for its speed and accuracy in reaching solution by searching global minima of six standard functions. Cyclical adjustment strategy was employed into the detected probability to increase searching ability. Meanwhile, the searching step was adaptively adjusted based on the optimal nest of the last generation and the current iteration numbers. Subsequently, ICS is used to estimate 7 sensitive parameters in ASM1 for practical applications. Field data are used to validate prediction accuracy of ASM1 with estimated parameters. Predicted results of the model are closer to the actual data with adjusted parameters.

Optimization of sampling strategy to determine pathogen removal efficacy of activated sludge treatment plant

Large-scale wastewater schemes rely on multi-barrier approach for the production of safe and sustainable recycled water. In multi-barrier wastewater reclamation systems, conventional activated sludge process (ASP) often constitutes a major initial treatment step. The main aim of this research was to determine most appropriate sampling approach to establish pathogen removal efficacy of ASP. The results suggest that ASP is capable of reducing human adenovirus (HAdV) and polyomavirus (HPyV) by up to 3 log₁₀. The virus removal data suggests that HAdV removal is comparable to somatic bacteriophage belonging to Microviridae family. Due to the high removal of Escherichia coli (>3 log₁₀) and very poor correlation with the enteric virus, it is not recommended that E. coli be used as a surrogate for enteric virus removal. The results also demonstrated no statistically significant differences (t test, P > 0.05) in calculated log removal values (LRVs) for HAdV, HPyV, and Microviridae from samples collected on hydraulic retention time (HRT) or simultaneous paired samples collected for influent and effluent. This indicates that a more practical approach of simultaneous sampling for influent and effluent could be used to determine pathogen removal efficiency of ASP. The results also suggest that a minimum of 10, preferably 20 samples, are required to fully capture variability in the removal of virus. In order to cover for the potential seasonal prevalence of viruses such as norovirus and rotavirus, sampling should be spread across all seasons.

Evaluation of a biological wastewater treatment system combining an OSA process with ultrasound for sludge reduction

Sludge production is an undesirable by-product of biological wastewater treatment. The oxic-settling-anaerobic (OSA) process constitutes one of the most promising techniques for reducing the sludge produced at the treatment plant without negative consequences for its overall performance. In the present study, the OSA process is applied in combination with ultrasound treatment, a lysis technique, in a lab-scale wastewater treatment plant to assess whether sludge reduction is enhanced as a result of mechanical treatment. Reported sludge reductions of 45.72% and 78.56% were obtained for the two regimes of combined treatment tested in this study during two respective stages: UO1 and UO2. During the UO1 stage, the general performance and nutrient removal improved, obtaining 47.28% TN removal versus 21.95% in the conventional stage. However, the performance of the system was seriously damaged during the UO2 stage. Increases in dehydrogenase and protease activities were observed during both stages. The advantages of the combined process are not necessarily economic, but operational, as US treatment acts as contributing factor in the OSA process, inducing mechanisms that lead to sludge reduction in the OSA process and improving performance parameters.

Modelling the link amongst fine-pore diffuser fouling, oxygen transfer efficiency, and aeration energy intensity

This research systematically studied the behavior of aeration diffuser efficiency over time, and its relation to the energy usage per diffuser. Twelve diffusers were selected for a one year fouling study. Comprehensive aeration efficiency projections were carried out in two WRRFs with different influent rates, and the influence of operating conditions on aeration diffusers' performance was demonstrated. This study showed that the initial energy use, during the first year of operation, of those aeration diffusers located in high rate systems (with solids retention time - SRT-less than 2 days) increased more than 20% in comparison to the conventional systems (2 > SRT). Diffusers operating for three years in conventional systems presented the same fouling characteristics as those deployed in high rate processes for less than 15 months. A new procedure was developed to accurately project energy consumption on aeration diffusers; including the impacts of operation conditions, such SRT and organic loading rate, on specific aeration diffusers materials (i.e. silicone, polyurethane, EPDM, ceramic). Furthermore, it considers the microbial colonization dynamics, which successfully correlated with the increase of energy consumption (r²:0.82 ± 7). The presented energy model projected the energy costs and the potential savings for the diffusers after three years in operation in different operating conditions. Whereas the most efficient diffusers provided potential costs spanning from 4900 USD/Month for a small plant (20 MGD, or 74,500 m³/d) up to 24,500 USD/Month for a large plant (100 MGD, or 375,000 m³/d), other diffusers presenting less efficiency provided spans from 18,000USD/Month for a small plant to 90,000 USD/Month for large plants. The aim of this methodology is to help utilities gain more insight into process mechanisms and design better energy efficiency strategies at existing facilities to reduce energy consumption.

Simultaneous nitrification/denitrification and stable sludge/water separation achieved in a conventional activated sludge process with severe filamentous bulking

This study investigated the long-term treatment performance of a conventional activated sludge (AS) process operating at a microaerobic DO level (0.5-1.0mg·L^-1) in the aeration tank and a long settling time of >10h in the clarification tank for sewage treatment. The microaerobic DO conditions led to severe sludge bulking. However, good sludge/water separation and excellent pollutant removal performance (COD, 95±2%; NH₄⁺-N, 99±1%; and TN, 69±6%) were stably achieved in the microaerobic AS system during its 150days of continuous operation. This is the first report to demonstrate that a long settling time effectively overcame the effect of severe filamentous bulking in conventional AS process, and that microaerobic DO conditions achieved excellent simultaneous nitrification and denitrification reactions in the aeration tank. The process characteristics of the microaerobic AS system differed substantially from those existing biological denitrification processes, including A/O, CANON, and OLAND processes.

Modelling effluent quality based on a real-time optical monitoring of the wastewater treatment process

A novel optical monitoring device was used for imaging an activated sludge process in situ during a period of over one year. In this study, the dependencies between the results of image analysis and the process measurements were studied, and the optical monitoring results were utilized to predict the important quality parameters for the wastewater treatment process efficiency: suspended solids, biological oxygen demand, chemical oxygen demand, total nitrogen and total phosphorous in biologically treated wastewater. The optimal subsets of variables for each model were searched using five variable selection methods. It was shown that online optical analysis results have clear dependencies on some process variables and the purification result. The model based on optical monitoring and process variables from the early stage of the treatment process can be used to predict the levels of important quality parameters, and to show the quality of the biologically treated wastewater hours in advance. This study confirms that the optical monitoring method is a valuable tool for monitoring a wastewater treatment process and receiving new information in real time. Combined with predictive modelling, it has the potential to be used in process control, keeping the process in a stable operating condition and avoiding environmental risks.

A comparative study of occurrence and fate of endocrine disruptors: diethyl phthalate and dibutyl phthalate in ASP- and SBR-based wastewater treatment plants

Phthalates are endocrine-disrupting chemicals which affect endocrine system by bio-accumulation in aquatic organisms and produce adverse health effects in aquatic organisms as well as human beings, when come in contact. Present study focuses on occurrence and removal of two phthalates: diethylphthalate (DEP) and dibutylphthalate (DBP) in two full-scale wastewater treatment plants (WWTPs) i.e. sewage treatment plants (STPs) based on well-adopted technologies, activated sludge process (ASP) and sequencing batch reactor (SBR).Gas chromatography-mass spectrometry (GC-MS) analysis was performed for both wastewater and sludge sample for determination and identification of the concentration of these compounds in both STPs by monitoring the STPs for 9 months. It was observed that the concentration of DEP was less than DBP in the influent of ASP and SBR. Average concentrations of DEP and DBP in sludge sample of ASP were found to be 2.15 and 2.08 ng/g, whereas in SBR plant, these values were observed as 1.71 and 2.01 ng/g, respectively. Concerning the removal efficiency of DEP, SBR and ASP plants were found effective with removal efficiency of 91.51 and 91.03 %, respectively. However, in the case of DBP, SBR showed lower removal efficiency (85.42 %) as compared to ASP (92.67 %). Comparative study of both plants proposed that in ASP plant, DBP reduction was higher than the SBR. Fourier transformation infrared (FTIR) analysis also confirmed the same result of sludge analysis for both STPs. Sludge disposal studied with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and thermo-gravimetric analysis (TGA) techniques confirmed that sludge of both STPs have high calorific value and can be used as fuel to make fuel-briquettes and bottom ash to make firebricks.

Adapting SimpleTreat for simulating behaviour of chemical substances during industrial sewage treatment

The multimedia model SimpleTreat, evaluates the distribution and elimination of chemicals by municipal sewage treatment plants (STP). It is applied in the framework of REACH (Registration, Evaluation, Authorization and Restriction of Chemicals). This article describes an adaptation of this model for application to industrial sewage treatment plants (I-STP). The intended use of this re-parametrized model is focused on risk assessment during manufacture and subsequent uses of chemicals, also in the framework of REACH. The results of an inquiry on the operational characteristics of industrial sewage treatment installations were used to re-parameterize the model. It appeared that one property of industrial sewage, i.e. Biological Oxygen Demand (BOD) in combination with one parameter of the activated sludge process, the hydraulic retention time (HRT) is satisfactory to define treatment of industrial wastewater by means of the activated sludge process. The adapted model was compared to the original municipal version, SimpleTreat 4.0, by means of a sensitivity analysis. The consistency of the model output was assessed by computing the emission to water from an I-STP of a set of fictitious chemicals. This set of chemicals exhibit a range of physico-chemical and biodegradability properties occurring in industrial wastewater. Predicted removal rates of a chemical from raw sewage are higher in industrial than in municipal STPs. The latter have typically shorter hydraulic retention times with diminished opportunity for elimination of the chemical due to volatilization and biodegradation.

Influence of hydraulic retention time on indigenous microalgae and activated sludge process

Integration of the microalgae and activated sludge (MAAS) process in municipal wastewater treatment and biogas production from recovered MAAS was investigated by studying the hydraulic retention time (HRT) of semi-continuous photo-bioreactors. An average total nitrogen (TN) removal efficiency (RE) of maximum 81.5 ± 5.1 and 64.6 ± 16.2% was achieved at 6 and 4 days HRT. RE of total phosphorous (TP) increased slightly at 6 days (80 ± 12%) HRT and stabilized at 4 days (56 ± 5%) and 2 days (55.5 ± 5.5%) HRT due to the fluctuations in COD and N/P mass ratio of the periodic wastewater. COD and organic carbon were removed efficiently and a rapidly settleable MAAS with a sludge volume index (SVI_10) of less than 117 mL g(-1) was observed at all HRTs. The anaerobic digestion of the untreated MAAS showed a higher biogas yield of 349 ± 10 mL g VS(-1) with 2 days HRT due to a low solids retention time (SRT). Thermal pretreatment of the MAAS (120 °C, 120 min) did not show any improvement with biogas production at 6 days (269 ± 3 (untreated) and 266 ± 16 (treated) mL gVS(-1)), 4 days (258 ± 11(untreated) and 263 ± 10 (treated) mL gVS(-1)) and 2 days (308 ± 19 mL (treated) gVS(-1)) HRT. Hence, the biogas potential tests showed that the untreated MAAS was a feasible substrate for biogas production. Results from this proof of concept support the application of MAAS in wastewater treatment for Swedish conditions to reduce aeration, precipitation chemicals and CO2 emissions.

Seasonal and diurnal variability of N2O emissions from a full-scale municipal wastewater treatment plant

During nitrogen removal in conventional activated sludge processes, nitrous oxide can be emitted. With a global warming potential of 298 CO2-equivalents it is an important greenhouse gas that affects the sustainability of wastewater treatment. The present study reports nitrous oxide emission data from a 16 month monitoring campaign on a full-scale municipal wastewater treatment. The emission demonstrated a pronounced diurnal and seasonal variability. This variability was compared with the variability of a number of process variables that are commonly available on a municipal wastewater treatment plant. On a seasonal timescale, the occurrence of peaks in the nitrite concentration correlated strongly with the emission. The diurnal trend of the emission coincided with the diurnal trend of the nitrite and nitrate concentrations in the tank, suggesting that suboptimal oxygen concentrations may induce the production of nitrous oxide during both nitrification and denitrification. This study documents an unprecedented dataset that could serve as a reference for further research.

Sorption and biodegradation of artificial sweeteners in activated sludge processes

There is limited information on the occurrence and removal of artificial sweeteners (ASs) in biological wastewater treatment plants, and in particular, the contribution of sorption and biodegradation to their removal. This study investigated the fate of ASs in both the aqueous and solid phases in a water reclamation plant (WRP). All the four targeted ASs, i.e. acesulfame (ACE), sucralose (SUC), cyclamate (CYC) and saccharine (SAC), were detected in both the aqueous and solid phases of raw influent and primary effluent samples. The concentrations of CYC and SAC in secondary effluent or MBR permeate were below their method detection limits. ACE and SUC were persistent throughout the WRP, whereas CYC and SAC were completely removed in biological treatment (>99%). Experimental results showed that sorption played a minor role in the elimination of the ASs due to the relatively low sorption coefficients (Kd), where Kd<500L/kg. In particular, the poor removal of ACE and SUC in the WRP may be attributed to their physiochemical properties (i.e. logKow<0 or logD<3.2) and chemical structures containing strong withdrawing electron functional groups in heterocyclic rings (i.e. chloride and sulfonate).

Fate and behavior of extended-spectrum β-lactamase-producing genes in municipal sewage treatment plants

Extended-spectrum β-lactamases (ESBLs) have the capability of hydrolyzing a variety of the newer β-lactam antibiotics, including the third-generation cephalosporins and monobactams known as a rapidly evolving group of ESBLs. The purpose of this study was to investigate the occurrence and fate of β-lactamase producing genes (CTX-M type 1, type2, CTX-M probe for all groups except CTX-M-1, and TEM, SHV, OXA) through wastewater treatment utilities. β-lactamase producing genes in influent, digested sludge, activated sludge, and disinfected effluent were monitored. The results showed that influent contained high level of all target genes, and all CTX-M types, SHV, and OXA gene decreased significantly in biological treatment process such as activated sludge process and anaerobic digestion, however, TEM type was not effectively eliminated. Possibly, host microbes of TEM could be most resistant in target genes or to some extent gene transfer occurred in wastewater treatment processes. All target genes were significantly reduced during disinfection. Consequently, wastewater treatment process apparently reduced host microbes carrying β-lactamase producing genes effectively, although they are selectively removed in biological processes. In addition, the significant reduction during disinfection was shown, although slightly differences of removal efficiency were observed in resistance.

Removal of endocrine-disrupting chemicals and conventional pollutants in a continuous-operating activated sludge process integrated with ozonation for excess sludge reduction

Sludge ozonation is considered as a promising technology to achieve a complete reduction of excess sludge, but as yet its effects on the removal of endocrine-disrupting chemicals (EDCs) and conventional pollutants (i.e., COD, N and P) in the activated sludge process are still unclear. In this study, two lab-scale continuous-operating activated sludge treatment systems were established: one was operated in conjunction with ozonation for excess sludge reduction, and the other was operated under normal conditions as control. The results indicate that an ozone dose of 100 mg O₃ g(-1)SS led to a zero yield of excess sludge in the sludge-reduction system during a continuous-operating period of 45d. Although ozonation gave a relatively lower specific oxygen uptake rate of activated sludge, it had little effect on the system's removal performance of COD and nitrogen substances. As a plus, sludge ozonation contributed a little more removal of target EDCs (estrone, 17β-estrodiol, estriol, 17α-ethinylestradiol, bisphenol A, and 4-nonylphenol). However, the total phosphorus removal declined notably due to its accumulation in the sludge-reduction system, which necessitates phosphorus recovery for the activated sludge process.